Which type of control cable must be used when pulleys change the direction of cable travel?

• A. Extra-flexible cable (7x19)
• B. Copper conductor
• C. Stainless steel 7x7
• D. Regular flexible cable

Answer: (A)

When a control cable must bend around pulleys, it needs to withstand repeated small bends without developing fatigue or kinking. Extra-flexible cable with a 7x19 construction achieves this because its many fine wires can move and flex together around curves, distributing the bending stress and allowing smooth operation around pulleys. The 7x19 design is significantly more flexible than a 7x7 arrangement, which is stiffer and more prone to fatigue at bends. Copper conductor isn’t a suitable choice for aircraft control cables due to corrosion and lower strength in this application; stainless steel 7x7 is strong but not as flexible as 7x19, and “regular flexible” doesn’t specify the level of flexibility required for multiple pulley turns. So the extra-flexible 7x19 cable is the best option for changing cable direction with pulleys.